The present invention generally relates to memory media and technologies for use with computers and other processing apparatuses. The invention particularly relates to solid-state mass storage devices using nonvolatile, solid-state memory components for permanent storage of data and methods of using capacitor-based power supplies thereon.
Nonvolatile, solid-state memory technologies are widely used in a variety of applications, nonlimiting examples including universal serial bus (USB) drives, digital cameras, mobile phones, smart phones, tablet personal computers (PCs), memory cards, and solid-state drives (SSDs). Nonvolatile, solid-state memory technologies used with computers and other processing apparatuses (referred to herein as host computer systems) are currently largely focused on NAND flash memory technologies, with other emerging nonvolatile, solid-state memory technologies including phase change memory (PCM), resistive random access memory (RRAM), magnetoresistive random access memory (MRAM), ferromagnetic random access memory (FRAM), organic memories, and nanotechnology based storage media such as carbon nanofiber/nanotube-based substrates. These and other nonvolatile, solid-state memory technologies will be collectively referred to herein as nonvolatile or solid-state media, memory components, or memory devices.
Mainly for cost reasons, at present the most common solid-state memory components used in SSDs are NAND flash memory components, commonly referred to as flash memory devices, flash memory components, flash-based memory devices, flash-based storage devices, flash-based media, or raw flash. As used herein, the term solid-state mass storage device refers to any device that uses nonvolatile, solid-state memory components for permanent storage of data and has means for providing for interaction between a host computer system and the memory components. A nonlimiting example of a solid-state mass storage device as used herein is a solid-state drive having a host interface for communicating with a host computer system, a memory controller, and an array of nonvolatile solid-state memory components (nonvolatile memory array) accessible by the memory controller for storing data of the host computer system therein.
For reasons of speed and performance, an SSD may include one or more volatile solid-state memory devices (hereinafter, volatile memory devices) for buffering or temporarily storing data intended to be stored on a nonvolatile memory array. In order not to affect performance, the data in the volatile memory devices may be only periodically flushed back to the nonvolatile memory array during operation, and when the solid-state mass storage device is properly shut down. If the power to the SSD were to be suddenly removed, the data in the volatile memory devices that has not yet been flushed to the nonvolatile memory array may be lost and unrecoverable.
Various measures have been implemented in the art to protect important data from being lost in the event of a power failure as described above. For example, an auxiliary power supply may be used to provide backup power in the event of primary power failure. Examples include an onboard battery or capacitor-based power supply located on the substrate (e.g., circuit board) of the SSD and integrated with the circuitry thereof. Typically, the auxiliary power supply (or module) is capable of providing power to the SSD for a time period sufficient for all outstanding data to be written to the nonvolatile memory array, and thereafter allow the memory controller to properly power down without the data potentially being lost.
More recently, supercapacitors have been used as auxiliary power supplies in SSDs. Unlike ceramic capacitors or aluminum electrolytic capacitors, supercapacitors, which include electrical double-layer capacitors (EDLCs), contain no conventional dielectric. Instead, an electrolyte (solid or liquid) ionically connects a pair of electrodes. In an EDLC supercapacitor, an electrical state called “electrical double layer” is defined as a pair of electrons and positive ions or a pair of holes and negative ions formed between an electrode and the electrolyte, and works as a dielectric and gives capacitance. Capacitance is proportional to the surface area of an electrode. Therefore, activated carbon is generally used for electrodes due to its large surface area, and enables supercapacitors to have a relatively high capacitance. The mechanism of ion absorption and desorption to and from the electrode surface contributes to charge and discharge of the supercapacitor. By applying voltage to the facing electrodes, ions are drawn to the surface of the electrode of opposite polarity, and the supercapacitor is charged. Conversely, the ions move away from the electrode surface when the supercapacitor is discharged. This process allows a supercapacitor to be charged and discharged repeatedly.
Supercapacitors located on SSDs are typically limited to being used as auxiliary power supplies for backup power. As such, these supercapacitors are generally not used during the normal operation of the SSD and remain fully charged. For example, U.S. Pat. No. 8,479,032 to Trantham et al. discloses a data-storage device having a power-reservoir circuit with a capacitor acting as an energy-storage device. The capacitor is designed to hold sufficient energy to provide substantially all of the primary operating power to memory devices of an SSD during a minimum time period sufficient to permit transfer of pertinent data from one or more volatile memory devices to one or more nonvolatile memory devices of the SSD. When a power-loss event is detected, power is provided to the memory devices and controllers from the power-reservoir circuit. To accomplish this function, a power-failure switch is used to control whether the primary-operating power is provided from the host-system power source or from the capacitor of the power-reservoir circuit. While not intending to promote any particular interpretation, it appears that the power-failure switch is not capable of providing primary operating power simultaneously from both the host system power source and the capacitor.
Supercapacitors can only provide a portion of their stored power in the event of a host power failure. Specifically, once the supercapacitor's voltage drops below the Under Voltage Lock Out (UVLO) level of the SSD, the supercapacitor can no longer provide power to the SSD and any residual energy within the supercapacitor cannot be extracted and utilized. That is, when the supercapacitor's voltage drops to the UVLO level, a power regulator inside the SSD will typically shut off because the input voltage is lower than a required level.
In view of the above, it can be appreciated that there are certain problems, shortcomings or disadvantages associated with the prior art, and that it would be desirable if a solid-state mass storage device were available that was equipped with a capacitor-based power supply capable of being utilized during the normal operation of the mass storage device and capable of supplying most if not all of its stored power to the mass storage device for a period of time in the event of a failure of the primary power supply.